The invention relates to a control device for controlling the engine speed of an internal combustion engine, in particular, of a two-stroke engine of a hand-held power tool such as a motor chainsaw, a cut-off device, a trimmer and the like. The internal combustion engine comprises an ignition control unit that controls the ignition timing of the spark plug relative to the crank angle of the crankshaft of the internal combustion engine as a function of the speed of the crankshaft. The engine further comprises a centrifugal clutch driven by the crankshaft that begins to engage when a first engine speed is surpassed and that is fully engaged when a second engine speed is reached.
Portable, hand-held power tools, for example, motor chainsaws, cut-off devices, trimmers and the like, are usually driven by a two-stroke engine whose spark plug is connected to an ignition control unit that controls the ignition timing relative to the crank angle of the internal combustion engine as a function of the speed of the crankshaft. A support for the flyweights of a centrifugal clutch is fixedly secured on the crankshaft, and the clutch bell of the centrifugal clutch is connected to an output shaft, an output gear or an output pulley or the like. When surpassing an engaging speed (first engine speed), the centrifugal clutch begins to engage and, after reaching a higher speed (second engine speed), it is essentially fully engaged without slip. When passing through this engine speed range, there is slip between the support with the flyweights and the clutch bell so that heat is generated. When the centrifugal clutch is operated with slip over an extended period of time in the range between the engaging speed and the fully engaged speed because of impermissible operating states, thermal overloads can occur that lead to impairment of the proper function of the centrifugal clutch.